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EPP Theory Seminar: Subir Sarkar (Oxford University) - A Test of the Cosmological Principle

In the ΛCDM cosmological model it is assumed that the universe is statistically isotropic and homogeneous when averaged on scales >100 Mpc. That the CMB has a large dipole anisotropy is explained as due to our 'peculiar motion' because of local inhomogeneity. There should then be a similar dipole in the sky distribution of high redshift sources. Using a catalogue of 1.4 million quasars we find this standard expectation is rejected at 4.9σ.

In the heliocentric frame the acceleration of the Hubble expansion rate too exhibits a dipole (at 3.9σ) aligned with the CMB. It is now questionable whether we can boost to the CMB frame to make the acceleration look isotropic and thus interpret it as due to Λ.


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